1. Field of the Invention
The present invention relates to an electroacoustic transducer, and, more particularly, to an electroacoustic transducer, which has an outer case formed integral with a lead frame previously formed into a predetermined shape and has some improvement on the structure of the terminal disposal section of a coil, thereby contributing to the reduction of the number of required parts, the simplification of the structure, the reduction of the size, and improvements on its performance and assembly efficiency.
2. Description of the Related Art
A variety of electroacoustic transducers include various types of electromagnetic type electroacoustic transducers. An electromagnetic type electroacoustic transducer as the first prior art is illustrated in FIGS. 11 and 12. There are an upper case 501 and a lower case 503, with a circular sound port 505 formed in the center of the top face of the upper case 501 in FIG. 11. A base 507, a printed circuit board 509 and a core 511 are accommodated in the lower case 503 in a securely integrated manner. A pair of pin-like lead terminals 513 and 515 are securely attached to the printed circuit board 509, and are led out of the board 509 downward in FIG. 11 by predetermined lengths.
A coil 517 is wound around the core 511, and a magnet 519 is placed around the coil 517 with a ring-like clearance formed in between. Formed at the upper end portion of the lower case 503 is a step portion 521 at which a diaphragm 522 is provided. This diaphragm 522 comprises an elastic plate (also called a resonance plate) 523 and a magnetic piece 525 attached as an added mass to the center portion of this elastic plate 523 on the upper case side.
In the thus constituted electromagnetic type electroacoustic transducer, the elastic plate 523 integrally provided with the magnetic piece 525 is set to have a given polarity by the magnet 519. When a current flows across the coil 517 via the lead terminals 513 and 515 under this situation, the core 511 is magnetized, generating a magnetic field at the distal end. When the magnetic pole of the core 511 induced by the coil 517 is the same as the magnetic pole induced by the magnet 519 attached to the elastic plate 523, the elastic plate 523 repels the core 511. When the former magnetic pole of the core 511 is different from the latter magnetic pole induced by the magnet 519, the elastic plate 523 is attracted to the core 511. By allowing the current to intermittently flow in either direction, therefore, the elastic plate 523 repeats the above-described operation. In other words, the elastic plate 523 vibrates at a given frequency, thus generating a sound.
This electromagnetic type electroacoustic transducer has a terminal connection structure of a coil as will be discussed below. As shown in FIG. 12, both coil terminals 517a and 517b of the coil 517 are led out on the printed circuit board 509 via an opening 507a formed in the base 507, and are securely soldered to lands 509a and 509b provided on the printed circuit board 509.
Positioning projections 527 and 529 protruding from the base 507 in FIG. 12 serve to position the printed circuit board 509 with respect to the base 507. This electromagnetic type electroacoustic transducer having the above-described structure is attached to a mounting board 531 indicated by an alternate one long and two short dashes line in FIG. 11 (which may be the mounting board of a portable telephone, a pager or the like if this electroacoustic transducer is incorporated into such a unit).
An electromagnetic type electroacoustic transducer as the second prior art will be discussed below with reference to FIGS. 13 and 14. A case 601 has a base member 603 attached to the bottom. A base 605 and a core 607 are integrally secured inside the base member 603. A coil 609 is wound around the core 607. A support ring 611 is provided inside the base member 603, and a magnet 613 is provided on the inner wall of this support ring 611. A ring-like clearance is formed between the magnet 613 and the coil 609. Formed at the left-hand end portion of the support ring 611 in FIG. 14 is a step portion 615 at which a diaphragm 616 is provided. This diaphragm 616 comprises an elastic plate (also called a resonance plate) 617 and a magnetic piece 619 attached as an added mass to the center portion of this elastic plate 617.
In the thus constituted electromagnetic type electroacoustic transducer, external connection terminals 621 and 623 have previously been attached in an integral manner to the base member 603 by insertion. In this case, as shown in FIG. 13, both coil terminals 609a and 609b of the coil 609 are led out on lands 621a and 623a (located in the base member 603) of the external connection terminals 621 and 623 and are securely soldered to those lands.
Since the action of this electromagnetic type electroacoustic transducer is the same as that of the electromagnetic type electroacoustic transducer illustrated in FIGS. 11 and 12, its description will not be repeated. The incorporation of this electromagnetic type electroacoustic transducer in a portable telephone, a pager or the like is the same as that of the first prior art; reference numeral "625" is given to the mounting board used for the incorporation as indicated by an alternate one long and two short dashes line in FIG. 14. In this case, the electroacoustic transducer is soldered at four places, namely the aforementioned external connection terminals 621 and 623 and attachment terminals 627 and 629 (shown in FIG. 13) which do not function electrically.
An electromagnetic type electroacoustic transducer as the third prior art will now be discussed with reference to FIG. 15. A case 701 has a circular sound port 703 formed in the center of the top face of the case 701 in FIG. 15. A base 705, a bobbin 707 and a core 709 are accommodated in the case 701 in a securely integrated manner. A pair of pin-like lead terminals 711 and 713 are attached to the bobbin 707, and are led through and out of the base 705 downward in FIG. 15 by predetermined lengths. A coil 715 is wound around the bobbin 707. A plastic magnet 717 is placed inside the case 701 with a ring-like clearance formed between the plastic magnet 717 and the coil 715.
Formed at the plastic magnet 717 is a step portion 719 at which a diaphragm 720 is provided. This diaphragm 720 comprises an elastic plate (also called a resonance plate) 721 and a magnetic piece 723 attached as an added mass to the center portion of this elastic plate 721 on the upper case side. In this case, both coil terminals 715a and 715b are led out toward the lead terminals 711 and 713, bound on them and secured by solder.
Since the action of this electromagnetic type electroacoustic transducer is the same as those of the electromagnetic type electroacoustic transducer illustrated in FIGS. 11 and 12 and the electromagnetic type electroacoustic transducer illustrated in FIGS. 13 and 14, its description will not be repeated. The incorporation of this electromagnetic type electroacoustic transducer in a portable telephone, a pager or the like is the same as that of the first prior art; reference numeral "725" is given to the mounting board used for the incorporation as indicated by an alternate one long and two short dashes line in FIG. 15.
The electroacoustic transducers according to the prior art have complicated structures and/or are large, which requires a greater number of parts and involves complicated assembling.
Those shortcomings will be discussed specifically. With regard to the electromagnetic type electroacoustic transducer according to the first prior art shown in FIGS. 11 and 12, both coil terminals 517a and 517b of the coil 517 are securely soldered to the lands 509a and 509b of the printed circuit board 509, and electrical inputs are made to the electroacoustic transducer via the pair of lead terminals 513 and 515 attached to the printed circuit board 509. This electroacoustic transducer therefore includes a greater number of components and requires a complicated structure at least in that it requires the printed circuit board 509.
As regards the electromagnetic type electroacoustic transducer according to the second prior art shown in FIGS. 13 and 14, the external connection terminals 621 and 623 are provided on a side portion of the drive section (which is constituted by the core 607, coil 609, magnet 613, elastic plate 617, magnetic piece 619, etc.) and both coil terminals 609a and 609b of the coil 609 are led out in the side portion of the drive section to be securely soldered to the lands 621a and 623a of the external connection terminals 621 and 623. This electroacoustic transducer needs planar space on the side portion of the drive section and thus becomes large. Moreover, at the time the coil terminals 609a and 609b are securely soldered to the lands 621a and 623a of the external connection terminals 621 and 623, the various components in the vicinity of the soldering portion interfere with the soldering work, thus deteriorating the workability.
The electromagnetic type electroacoustic transducer according to the third prior art shown in FIG. 15 is a bobbin type which essentially uses the bobbin 707. This inevitably increases the number of required components, complicates the structure and increases the overall size.
In considerations of the recent demands for smaller devices of various kinds which incorporate an electromagnetic type electroacoustic transducer, such as portable telephones and pagers, there are strong demands for smaller electromagnetic type electroacoustic transducers with simpler structures.